Optical properties of dense self-assembled gold nanoparticle layers with organic linker molecules

Films consisting of self-assembled gold nanoparticles cross-linked with alkane-dithiols were prepared by a filtration method and studied with scanning electron microscopy to determine the structure of the films and spectrophotometry and ellipsometry to ascertain their optical properties. The structural characterization showed the existence of nanometer sized voids within the films. This previously unmentioned feature is responsible for the previous difficulties in modelling the optical properties with effective medium models.This can be remedied, using a two-tiered hierarchical effective medium model, which takes into account the existence of the voids. Using this model we were able to fit the experimental data,with only the void volume fraction to be determined by the overall fit, while the gold volume fraction in the linker medium is fixed by the wavelength of the resonance peak. Our model should be applicable to all such films, when the deposition method, which determines the microstructure, is properly taken into account.

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